I understand what you're saying.
Got home and checked some of my sight leaf pieces, which I already knew what I would find. Have an IP with RP base and RP leaf which is identical in milling to the ebay flip in every way. These two leafs are different from most other ones, but I'm sure my IP leaf is real. And neither this or the ebay one match the High Quality reproductions milling that we see.
EDIT: thought I had a Sag with a Square S with the same overall leaf milling (which would've surprised me), but it's an honest original and is not the same. By milling I'm talking all aspects.
So I've got an IP marked RP/RP just like the ebay one. I'm still just as solid that the ebay one is all real.
This is a fake IP sight. M1 Carbine Parts Type 1 Flip Sight Irwin Pedersen Marked B IP 99 | eBay